4/22/2002 George Wai Wong 1 Future Mobile Communications beyond 3G Systems A Multicarrier CDMA Architecture Based on Orthogonal Complementary Codes Prepared

4/22/2002George Wai Wong 1

Future Mobile Communications beyond 3G Systems

A Multicarrier CDMA Architecture Based on Orthogonal Complementary Codes

Prepared for EECE565 – Wireless Communication Systems


Maturity of 3G Systems

• Extensive evaluation of W-CDMA has been carried out in both simulations and field trials.

• In May 2001, Japan initiated the world’s first testing commercial services for 3G mobile communications based on W-CDMA.


Maturity of 3G Systems (cont.)

• The first 3G networks based on CDMA2000 technology were launched in Korea in October 2000.


Maturity of 3G systems (cont.)

• CDMA2000 terminal products are already available in the market.


4G mobile communications

• At the time of this presentation, nobody is very sure what 4G will look like.

• Systems beyond 3G ought to deliver a much higher data rate which should be roughly in range of 10 to 100Mbps


High data rate in mobile channel

• Mobile communication channels are highly unpredictable. (This is why EECE563 final exam is so unpredictable)

• Questions are:1. how to guarantee such a high data rate in mobile

communication channel

2. what types of air link architecture are qualified to deliver high-data-rate services


New CDMA architecture

• The new CDMA architecture ought to be technically feasible and should not introduce too much multiple access interference (MAI).

• The multicarrier CDMA architecture based on orthogonal complete complementary code (CC) code can satisfy the above-mentioned requirements.


Complete Complementary Code

• CC code is based on a “flock” of elements codes instead of a single code as in traditional CDMA codes.

• In other words, every user in the proposed CDMA system will be assigned a flock of elements codes as its signature code which must be transmitted possibly via different channels


CC Code (cont.)Element code length L=4 Element code length L = 16

Flock 1 A0: + + - - Flock 1 A0: + + + + + - + - + + - - + - - +

A1: + - + - + + + + + - - + + + - -

A2: + + - - + - - + + + + + + - + -

A3: + - - + + + - - + - + - + + + +

A1: + - + + Flock 2 B0: + + + + - + - + + + - - - + + -

B1: + - + - - - - - + - - + - - + +

B2: + + - - - + + - + + + + - + - +

B3: + - - + - - + + + - + - - - - -

Flock 2 B0: + + - + Flock 3 C0: + + + + + - + - - - + + - + + -

C1: + - + - + + + + - + + - - - + +

C2: + + - - + - - + - - - - - + - +

C3: + - - + + + - - - + - + - - - -

B1: + - - - Flock 4 D0: + + + + - + - + - - + + + - - +

D1: + - + - - - - - - + + - + + - -

D2: + + - - - + + - - - - - + - + -

D3: + - - + - - + + - + - + + + + +


MAI-free operationSignature for user 1: A0 = + + + - and A1: + - + +

Signature for user 1: B0 = + + - + and B1: + - - -

Spreading modulated signal for user 1 (assume the information bits are all +)

0

0

0

8

0

0

0

means ‘+’

means ‘-’

A0: A1:

f1 f2


MAI-free operation (cont.)Signature for user 1: A0 = + + + - and A1: + - + +

Signature for user 1: B0 = + + - + and B1: + - - -

Spreading modulated signal for user 2 (assume the information bits are all +)

means ‘+’

means ‘-’

A0: A1:

f1 f2

0

0

0

0

0

0

0


Bit error rate in AWGN channel

• Downlink BER comparison (synchronized channel)

• Length of Gold code, M-sequence code, and CC code are 63, 63, 4 x 16 respectively

• Note that the new CDMA system has almost identical BER performance regardless of the number of users


Bit error rate in AWGN channel (cont.)

• Uplink BER comparison (approximately synchronized channel)

• Lengths of Gold code, M-sequence code, and CC code are 63, 63, 4 x 16, respectively.

• At least 2dB is obtainable from the proposed CDMA system


Bandwidth efficiency

• In traditional DS-CDMA techniques, the spreading efficiencies (SEs) are equal to 1/N, where N is denoted as the length of a spreading code

• In the proposed CDMA system, the SEs are much higher compare to the traditional DS-CDMA systems.


Bandwidth efficiency (cont.)

PG 8 64 512 4096 32768 262144

Conventional CDMA

1/8 1/64 1/512 1/4096 1/32768 1/262144

CC-code-based CDMA

1/2 1/4 1/8 1/16 1/32 1/64

CC-code-based CDMA (orthogonal carriers)

1 1/2 1/4 1/8 1/16 1/32


Technical limitations

• Given the element code length L of the CC code, it is necessary to choose a digital modem capable of transmitting L+1 different levels

• If a long CC code is employed in the proposed CDMA system, the number of different levels generated from a baseband spreading modulator can be a problem!!!

• One possible solution to this problem is to use (L+1)-QAM digital modem


Technical limitations (cont.)

• A relatively small number of users can be supported by a family of CC codes.

Element code length (L=4n) 4 16 64 256 1024 4096

PG( L L) 8 64 512 4096 32768 262144

Family size L 2 4 8 16 32 64

Flock size 2 4 8 16 32 64

• One possible solution to this problem is to introduce frequency divisions on top of the code division to create more transmission channel.


Conclusions

• The proposed CDMA system offers much higher bandwidth efficiency than traditional CDMA systems.

• It also offers MAI-free operation in both up- and downlink channels.

• The BER of the proposed CDMA system under MAI and AWGN channel is relatively lower than traditional CDMA systems.


Conclusions (cont.)

• The technical limitations of the proposed CDMA system are a relatively small family of CC codes and the need for complex multilevel digital modem.

• Nevertheless, the proposed CDMA architecture based on complete complementary codes offers a new option to implement future wideband mobile communications beyond 3G.


References

• H. H. Chen; J. F. Yeh; N. Suehiro, “A multicarrier CDMA architecture based on orthogonal complementary codes for new generations of wideband wireless communications,” IEEE Commun. Mag., vol 39, no. 10, Oct. 2001, pp. 126 –135

• N. Suehiro, “Complementary Code Composed of N-Multiple-Shift Orthogonal Sequences,” Trans IECE, vol. J65-A, Dec. 1982, pp. 1247-53.

• T. Imoto, N. Suehiro, N. Kuroyanag, R. Fan, “Avoidance of inter-cell interference on approximately synchronized CDMA without co-channel interference nor multipath fading using complete complementary code,” Spread Spectrum Techniques and Applications, 2000 IEEE Sixth International Symposium on, vol. 1, 2000, pp. 102 –106.

• E. H. Dinan and B. Jabbari, “Spreading Codes for Direct Sequence CDMA and Wideband CDMA Cellular Networks,” IEEE Commun. Mag., vol 36, no. 9, Sept. 1998, pp. 55-81


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4/22/2002 George Wai Wong 1 Future Mobile Communications beyond 3G Systems A Multicarrier CDMA Architecture Based on Orthogonal Complementary Codes Prepared